Digital-analog conversion apparatus and method

ABSTRACT

An apparatus and a method for digital-analog conversion are provided. The apparatus includes a first cell matrix for outputting a current of a signal corresponding to a number of Most Significant Bits (MSBs) of an input digital signal, a second cell matrix for outputting a current of a signal corresponding to a number of Least Significant Bits (LSBs) of the input digital signal, an amplifier for amplifying the output current of the second cell matrix at a preset amplification, and an adder for adding the output current of the first cell matrix and the output current of the amplifier.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on Dec. 6, 2011 in the Korean IntellectualProperty Office and assigned Serial No. 10-2011-0129551, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital-analog converter forconverting a digital signal to an analog signal.

2. Description of the Related Art

As digital signal processing techniques advance, signal processingtechniques for converting an analog signal into a digital signal andconverting the digital signal back into the analog signal are widelyused and amounts of data processing used by various wired and wirelesscommunication systems using the signal processing is increasing. Hence,an amount of digital signals to be converted to analog signals isincreasing, and a digital-analog converter having a high conversionspeed and high resolution is needed.

Digital-analog converters which sample an input signal at a Nyquist rateare provided by related art. Such digital-analog converters may achievehigh resolution in theory as a number of bits increases, but it isdifficult to attain a high resolution over 6 bits because of distortionarising from fabrication error. Digital-analog converters which producethe analog signal by combining current cells according to the input bitsare also provided by the related art. The combination of the currentcells allows for relatively low fabrication error and thus realizes adigital-analog converter of high resolution bits. However, an N-bitdigital-analog converter requires 2^(N)−1-ary current cells.Accordingly, the more bits, the more current cells needed. Furthermore,as the number of the current cells increases, a total area of thedigital-analog converter expands and thus an Integrated Non-Linearity(INL) error may increase.

Accordingly, a related art method may reduce the INL error by randomlychanging a pointer according to an input signal level every hour andusing a different current cell every hour. However, the related artmethod may not reduce a Differential Non-Linearity (DNL) errorindicating an error between the current cells, and thus reliability ofthe output signal per hour may be degraded. Furthermore, when ahigh-resolution digital-analog converter over 10 bits is realized usingthe related art method, more than 1,023 cells are necessary. As aresult, implementing a circuit for randomly using more than 1,023 cellsmay need a complicated manufacturing process and a manufacturing costrises due to the increase of the total area of the digital-analogconverter.

Therefore, a need exists for a system and method for a digital-analogconverter having a high conversion speed and high resolution.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide an apparatus and a method of a digital-analogconverter.

Another aspect of the present invention is to provide an apparatus of adigital-analog converter including a cell matrix which divides an inputdigital signal into two or more groups and outputs a current of eachgroup, and a method of the digital-analog converter.

Yet another aspect of the present invention is to provide a method andan apparatus for reducing an Integrated Non-Linearity (INL) error and aDifferential Non-Linearity (DNL) error using a cell matrix which drivesa plurality of cells arranged symmetrically for arbitrary input bits ina digital-analog converter.

Still another aspect of the present invention is to provide a method andan apparatus for estimating a fabrication error and correcting theestimated error in an initial driving of a digital-analog converter.

In accordance with an aspect of the present invention, an apparatus fordigital-analog conversion is provided. The apparatus includes a firstcell matrix for outputting a current of a signal corresponding to anumber of Most Significant Bits (MSBs) of an input digital signal, asecond cell matrix for outputting a current of a signal corresponding toa number of Least Significant Bits (LSBs) of the input digital signal,an amplifier for amplifying the output current of the second cell matrixat a preset amplification, and an adder for adding the output current ofthe first cell matrix and the output current of the amplifier.

In accordance with another aspect of the present invention, a method ofa digital-analog converter is provided. The method includes dividing aninput digital signal into a Most Significant Bit (MSB) signalcorresponding to a number of MSBs and a Least Significant Bit (LSB)signal corresponding to a number of LSBs, outputting a current for theMSB signal using a first cell matrix, outputting a current for the LSBsignal using a second cell matrix, amplifying the output current usingthe second cell matrix at a preset amplification, and adding the outputcurrent of the first cell matrix and the amplified output current andoutputting a result of the adding.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a digital-analog converter according to an exemplaryembodiment of the present invention; and

FIG. 2 illustrates operations of the digital-analog converter accordingto an exemplary embodiment of the present invention.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

Exemplary embodiments of the present invention provide an apparatus anda method of a digital-analog converter including a cell matrix whichdivides an input digital signal to two or more groups and outputs acurrent of each group. Hereinafter, to ease the understanding, adigital-analog converter for current regulation is explained by way ofexample. Notably, a cell matrix structure of the present invention isequally applicable to other digital-analog converters using the cellmatrix. To facilitate the understanding, an input digital signal isdivided into a certain number of Most Significant Bits (MSBs) and acertain number of Least Significant Bits (LSBs) by way of example. Thepresent method can be equally applied to the input digital signal whichis divided into two or more groups.

FIG. 1 illustrates a digital-analog converter according to an exemplaryembodiment of the present invention.

Referring to FIG. 1, the digital-analog converter includes a firstthermometer decoder 100 for processing a signal of the certain number ofthe MSBs, a first switching matrix 110, a first cell matrix 120, asecond thermometer decoder 102 for processing a signal of the certainnumber of the LSBs, a second switching matrix 112, a second cell matrix122, an amplifier 132, an adder 130, and an error detector 134. Withrespect to the digital-analog converter of FIG. 1, an input K-bitdigital signal is divided into N-ary MSBs and M-ary LSBs, and K=10, N=5,and M=5. Notably, the MSBs N and the LSBs M may be set to differentvalues according to a design and thus a number of current cells of acell matrix may vary, as will be described below.

The first thermometer decoder 100 may convert the input N-bit digitalsignal, which is generated from the K-bit digital signal which is inputto the digital-analog converter, into a signal of 2^(N)−1-aryconsecutive bits, and outputs the converted bit signal to the firstswitching matrix 110. For example, when a 5-bit MSB signal of “00011” isinput, the first thermometer decoder 100 may convert “00011” into asignal of 31(2⁵−1)-ary consecutive bits that is“0000000000000000000000000000111”. Furthermore, when a 5-bit MSB signalof “00101” is input, the first thermometer decoder 100 may convert“00101” into a signal of 31(2⁵−1)-ary consecutive bits that is“0000000000000000000000000011111”. The consecutive bit values may beoutput in parallel to correspond with a plurality of switches (notshown) of the first switching matrix 110.

The first switching matrix 110 may include switches (not shown) for aplurality of cells of the first cell matrix 120, and thus, may supply orcut-off a current source of the cells. That is, the first switchingmatrix 110 may determine a cell to which the current source is suppliedaccording to the consecutive-bit signal output from the firstthermometer decoder 100, and may turn a switch of the corresponding cellON or OFF. In particular, for a one-bit signal, the first switchingmatrix 110 may controls the current source supply of four symmetriccells in the first cell matrix 120. For example, when a signalcorresponding to “0000000000000000000000000000011” is input to the firstswitching matrix 110 from the first thermometer decoder 100, then thefirst switching matrix 110 may recognize two bits having the value ‘1’and may control supplying of the current source by switching two cellsin each of four subcell matrixes 120-1 through 120-4 ON or OFF, whereinthe four subcell matrixes 120-1 through 120-4 are symmetrical to eachother in both a vertical direction and a horizontal direction. That is,first and second cells of each of the four subcell matrixes 120-1through 120-4 may be switched to an ON or OF state.

In order to determine the cell to which the current source is suppliedaccording to the input signal bits, the first switching matrix 110 maydetermine the cell according to a predefined procedure or at random.Notably, the first switching matrix 110 may control the current sourceto be simultaneously supplied to or cut-off from the symmetric cells ofthe four subcell matrixes 120-1 through 120-4. In other words, the firstswitching matrix 110 may cut-off the current source for only some of thesymmetric cells of the four subcell matrixes 120-1 through 120-4, or thecurrent source may be supplied to the symmetric cells at differenttimes. When the first switching matrix 110 is initially turned on, itmay conduct the switching to supply the current source to one of thecells of the first cell matrix 120 according to a request of the errordetector 134 so as to detect a fabrication error.

The first cell matrix 120 may output a current corresponding to theN-MSB digital signal that is generated from the K-bit digital signalwhich is input to the digital-analog converter. The first cell matrix120 may include the four subcell matrixes 120-1 through 120-4, which aresymmetrical to each other in both in the vertical direction and thehorizontal direction. The subcell matrixes 120-1 through 120-4 eachinclude 2^(N)−1-ary current cells. The cells may output the same currentwhen the current source is supplied to the cells of the first cellmatrix 120.

The second thermometer decoder 102 may convert the input M-bit digitalsignal, which is generated from the K-bit digital signal which is inputto the digital-analog converter, into a signal of 2^(M)−1-aryconsecutive bits, and may output the converted bit signal to the secondswitching matrix 112. For example, when a 5-bit LSB signal of “00110” isinput, the second thermometer decoder 102 may convert “00110” to asignal of 31 consecutive bits that is “0000000000000000000000000111111”.Accordingly, the consecutive bit values may be output in parallel so asto correspond with a plurality of switches of the second switchingmatrix 112. In particular, the second thermometer decoder 102 maycorrect a fabrication error by adding or subtracting a digital bit,which indicates the fabrication error, to or from the input M-bitdigital signal value under control of the error detector 134. Forexample, under the control of the error detector 134, the secondthermometer decoder 102 may correct the input 5-bit LSB signal “00110”to be “00111” by adding 1 and may convert to the consecutive 31-bitsignal corresponding to “00111”, or may correct the input 5-bit LSBsignal “00110” to be “00101” by subtracting 1 and convert to theconsecutive 31-bit signal corresponding to “00101”.

The second switching matrix 112 may include a plurality of switches fora plurality of cells of the second cell matrix 122, and thus may supplyor cut-off the current source of the cells. That is, the secondswitching matrix 112 may determine a cell to supply the current sourceaccording to the consecutive-bit signal output from the secondthermometer decoder 102, and may turn ON or OFF the switch of thecorresponding cell. In particular, the second switching matrix 112 maycontrol the current source supply of four symmetric cells of the secondcell matrix 122. For example, when a signal corresponding to“0000000000000000000000000111111” is input from the second thermometerdecoder 102 to the second switching matrix 112, then the secondswitching matrix 112 may recognize six bits having the value ‘1’ and maycontrol supplying of the current source by switching six cells in eachof four symmetric subcell matrixes 122-1 through 122-4, which are thefirst through sixth cells of the four subcell matrixes 122-1 through122-4. In order to determine the cell that the current source issupplied to according to the input signal bits, the second switchingmatrix 112 may determine the cell according to a predefined procedure orat random. The second switching matrix 112 may control the currentsource to be simultaneously supplied to or cut-off from the symmetriccells of the four subcell matrixes 122-1 through 122-4. Additionally,when the second switching matrix 112 is initially turned on, it mayconduct the switching to supply the current source to a certain numberof cells from among the cells of the second cell matrix 122 according toa request of the error detector 134 so as to detect the fabricationerror.

The second cell matrix 122 may output the current corresponding to theM-bit digital signal, which is for the LSBs and is generated from theK-bit digital signal which is input to the digital-analog converter. Thesecond cell matrix 122 may include the four subcell matrixes 122-1through 122-4 which are symmetric to each other in both the verticaldirection and the horizontal direction. The subcell matrixes 122-1through 122-4 may each include 2^(M)−1-ary current cells. In a casewhere the current source is supplied to the cells of the second cellmatrix 122, then the cells output the same current. Additionally, insuch a case, all of the cells of the second cell matrix 122 and thefirst cell matrix 120 output the same current. Furthermore, the subcellmatrixes 122-1 through 122-4 of the second cell matrix 120 may furtherinclude cells in addition to the 2^(M)−1-ary current cells so as tocorrect the fabrication error.

The amplifier 132 may amplify the current output from the second cellmatrix 122 at a preset amplification or at any suitable amplification,and may output the amplified current. In so doing, the amplification maybe determined by the number M of the LSBs. That is, the amplifier 132may amplify the current output from the second cell matrix 122 at theamplification of

$\frac{1}{2^{M}}.$Herein, the output current of the second cell matrix 122 may beamplified according to the number M of the LSBs because the outputcurrent of the cells of the first cell matrix 120 may be M times greaterthan the output current of the cells of the second cell matrix 122,wherein the output currents may be different because the N-MSB signal isinput to the first cell matrix 120 and the M-LSB signal is input to thesecond cell matrix 122 while the cells of the first cell matrix 120 andthe cells of the second cell matrix 122 output the same current. Thus,the signal may be attenuated using an attenuator (not shown), instead ofthe amplifier 132, at a preset attenuation, or any suitable attenuation,according to the design. The output current of the first cell matrix 120may be amplified 2^(M) times, rather than regulating the output currentof the second cell matrix 122.

The adder 130 may add the output current of the first cell matrix 120and the amplified current output from the second cell matrix 122 inorder to provide the output of the digital-analog converter. The adder130 may be configured to add the output and amplified current of thesecond cell matrix 122 to the output current of the first cell matrix120 using a current mirror (not shown). However, the present inventionis not limited thereto, and the adder 130 may add signals and/orcurrents in any suitable manner.

The error detector 134 may detect the error in the fabrication, i.e.,the fabrication error, and may correct a signal by considering thedetected error. Particularly, the error detector 134 may detect thefabrication error using a property of the digital-analog converter ofthe present exemplary embodiments, wherein the current value output fromone unit cell of the first cell matrix 120 should be equal to thecurrent value produced by amplifying the output currents of all of thecells of the second cell matrix 122 at the preset amplification. Theunit cell may include the symmetric cells in the corresponding cellmatrix. For example, the first unit cell of the first cell matrix 120may include the first cell of the first subcell matrix 120-1, the firstcell of the second subcell matrix 120-2, the first cell of the thirdsubcell matrix 120-3, and the first cell of the fourth subcell matrix120-4.

Accordingly, when the digital-analog converter is turned on, the errordetector 134 may output a control signal to the first switching matrix110 and the second switching matrix 112, wherein the control signalcorresponds to the fabrication error correction, and then the errordetector 134 may receive the current output from one unit cell of thefirst cell matrix 120, may receive the current amplified at the presetamplification from the second cell matrix 122, may compare the twocurrents, and thus, the error detector 134 may detect the error. In sodoing, the first cell matrix 120 may output the current of thecorresponding unit cell by driving one unit cell, which may bearbitrarily selected, by the control signal of the error detector 134.By contrast, the second cell matrix 122 may change the number of theunit cells driven by the control signal of the error detector 134 andmay output the current according to the number of the driven unit cells.Thus, the error detector 134 may compare the current fed from the firstcell matrix 120 and the current fed from the second cell matrix 122using a comparator (not shown), and thus the error detector 134 maydetect the fabrication error based on the number of the driving unitcells of the second cell matrix 122 corresponding to the time when thetwo currents are equal, which is also the time when the output result ofthe comparator changes.

For example, the current amount of the first unit cell of the first cellmatrix 120 should be equal to the current amount of the 31 first unitcells of the second cell matrix 122. When the second cell matrix 122drives 29 unit cells, the comparator may output a low value. However,when the second cell matrix 122 drives 30 unit cells, the comparator mayoutput a high value. In such a case, the error detector 134 maydetermine that the current amount that is output when the second cellmatrix 122 drives the 30 unit cells is equal to the current amountoutput when the first cell matrix 120 drives one unit cell. Accordingly,since the output current amount of all of the cells of the second cellmatrix 122 is greater than the unit cell current amount of the firstcell matrix 120, then the error detector 134 may decrease the outputcurrent of the second cell matrix 122 for the correction. The errordetector 134 may correct the output current by subtracting 1 from theinput digital signal in the second thermometer decoder 102 of the secondcell matrix 122 and may drive the unit cells which are one unit cellsmaller than the unit cells corresponding to the input digital signal inthe second cell matrix 122, or may correct the output current byregulating a bias current source supplied to the second cell matrix 122.

For example, in a case where the second cell matrix 122 drives the 31unit cells and the comparator outputs the low value, the second cellmatrix 122 may drive additional cells besides the 31 cells. Accordingly,when the second cell matrix 122 drives 32 unit cells in total includingthe 31 unit cells and the additional unit cell and the comparatoroutputs the high value, the error detector 134 may determine that thecurrent amount output when the second cell matrix 122 drives the 32 unitcell is equal to the current amount output when the first cell matrix120 drives one unit cell. Since the output current amount of the secondcell matrix 122 may be smaller than the unit cell current amount of thefirst cell matrix 120, the error detector 134 may increase the outputcurrent of the second cell matrix 122 for the correction. The errordetector 134 may correct the output current by adding 1 to the inputdigital signal in the second thermometer decoder 102 for the second cellmatrix 122 and may drive the unit cells which are one unit cell greaterthan the unit cells corresponding to the input digital signal in thesecond cell matrix 122, or the error detector 134 may correct the outputcurrent by regulating a bias current source supplied to the second cellmatrix 122.

While each cell matrix may include four subcell matrixes as illustratedin FIG. 1, any of the cell matrixes may include only one subcell matrix,two vertically symmetric subcell matrixes, or two horizontally symmetricsubcell matrixes according to its design.

Referring to FIG. 1, the input signal may be divided into the two groupsfor example. In a case where the input signal is divided into threegroups, the digital-analog converter may use thermometer decoders,switching matrixes, and cell matrixes for the three groups,respectively, and may use an amplifier or an attenuator for regulatingthe output currents of the cell matrixes for two groups from among thecell matrix output of the three groups. The digital-analog converter mayalso use an adder for adding the outputs of the cell matrixes of thethree groups, and may use an error detector for estimating thefabrication error.

FIG. 2 illustrates operations of a digital-analog converter according toan exemplary embodiment of the present invention.

Referring to FIG. 2, it may be assumed that the digital-analog converterincludes the two cell matrixes which divides and processes the K-bitinput digital signal into the N MSBs and the M LSBs as shown in FIG. 1.However, the present invention is not limited thereto, and there may bemore than two cell matrixes included in the digital-analog converter ofFIG. 2. In operation 201 the digital-analog converter is turned on, andthen, in operation 203, it may detect and store a fabrication error. Thefabrication error may indicate an error caused by a variety of factors,such as silicon thickness or texture, when the digital-analog converteris designed. The digital-analog converter may define a reference currentby driving one unit cell in the first cell matrix 120, output thecurrent while changing the number of the unit cells driven in the secondcell matrix 120, amplify the output current at the preset amplification,and compare values or amounts of the amplified current and the referencecurrent, and thus, the digital-analog converter may detect thefabrication error. The fabrication error may be determined according toa difference between the number of the unit cells driven in the secondcell matrix 122 and the number 2^(M)-1 of the unit cells of the secondcell matrix 122 when the current of the second cell matrix 122, asoutput and amplified, becomes equal to the reference current. Forexample, when the second cell matrix 122 including the 31 unit cellsdrives 30 unit cells and the current that is output and amplified isequal to the reference current, then the fabrication error may be −1LSB. In a case where the second cell matrix 122, which includes the 31unit cells, drives the 31 unit cells and further drives one additionalunit cell, which is used for an exceptional situation, and the currentthat is output and amplified is equal to the reference current, then thefabrication error may be +1 LSB.

Next, in operation 205, the digital-analog converter may divide theinput digital signal into the N MSBs and the M LSBs, and then may inputthe digital signal of the N MSBs to the first thermometer decoder 100and input the digital signal of the M LSBs to the second thermometerdecoder 102. In operation 207, the digital-analog converter may convertthe digital signal of the N MSBs to the signal of the consecutive2^(N)−1-ary bits via the first thermometer decoder 100, and may convertthe digital signal of the M LSBs to the signal of the consecutive2^(M)−1-ary bits via the second thermometer decoder 102. For example, ina case where the digital signal input to the digital-analog converter is10-bit “0010101111”, the digital-analog converter may split the 10-bitdigital signal into the 5 MSBs “00101” and the 5 LSBs “01111”, mayconvert the 5 MSBs “00101” into the signal of 31(2⁵−1)-ary consecutivebits that is “0000000000000000000000000011111”, and may convert the 5LSBs “01111” to the signal of 31(2⁵−1)-ary consecutive bits that is“0000000000000000111111111111111”. Herein, the signal of the31(2⁵−1)-ary consecutive bits may indicate the number of the cells thatare to be driven in the corresponding cell matrix.

Next, in operation 209, the digital-analog converter may correct thesignal of the consecutive 2^(M)−1-ary bits of the M LSBs by consideringthe detected fabrication error. For example, in a case where thefabrication error detected in operation 203 is −1, the digital-analogconverter may determine to drive the unit cells with one less cell. Inorder to do so, the digital-analog converter may convert theconsecutive-bit signal that is “0000000000000000111111111111111” into aconsecutive bit signal that is “0000000000000000011111111111111”. Forexample, before converting the digital signal of the M LSBs to thesignal of the consecutive 2^(M)−1-ary bits, the digital-analog convertermay subtract 1 from the digital signal of the M LSBs and may convert thesubtraction result to the signal of the consecutive 2^(M)−1-ary bits.

In operation 211, the digital-analog converter may output the current bydriving a number of the unit cells that corresponds to the numberindicated by the signal of the consecutive 2^(N)−1-ary bits in the firstcell matrix 120, and may output the current by driving another number ofthe unit cells that corresponds to the number indicated by the signal ofthe consecutive 2^(M)−1-ary bits in the second cell matrix 122.Accordingly, the unit cells of the first cell matrix 120 and the unitcells of the second cell matrix 122 are driven at the same timeaccording to a reference clock under the control of the respectiveswitching matrixes 110 and 112.

In operation 213, the digital-analog converter may amplify the outputcurrent of the second cell matrix 122 at the preset amplification of

$\frac{1}{2^{M}}.$Accordingly, the output current of the second cell matrix 122 may beamplified because the output current of the cells of the first cellmatrix 120 may be M times greater than the output current of the cellsof the second cell matrix 122 since the N-bit digital signal of MSBs maybe input to the first cell matrix 120 and the M-bit digital signal ofLSBs may input to the second cell matrix 122 while the cells of thefirst cell matrix 120 and the cells of the second cell matrix 122 outputthe same current. Thus, the digital-analog converter may attenuate thesignal of the second cell matrix 122 at the preset attenuation accordingto the design. The digital-analog converter may amplify the outputcurrent of the first cell matrix 120 by 2^(M) times, rather thanregulating the output current of the second cell matrix 122.

Next, in operation 215, the digital-analog converter may add the outputcurrent of the first cell matrix 120 and the current that is output andamplified by the second cell matrix 122. Next, the digital-analogconverter returns to operation 205. While the thermometer decoder 102may correct the fabrication error by controlling the digital signal, asillustrated in FIG. 2, the fabrication error may also be corrected bycontrolling the bias current source supplied to the second cell matrix122.

As set forth above, the digital-analog converter may include two or morecell matrixes for dividing and processing the input digital signal intotwo or more groups. Thus, a total area of the digital-analog convertermay be reduced by decreasing the number of the unit cells as compared tothe number of the input bits, and thus, manufacturing costs may bedecreased as compared to a related art digital-analog converter.Furthermore, the cell matrix may drive the plurality of the symmetriccells for arbitrary input bits, may estimate a fabrication error at aninitial driving of the cell matrix, and may then correct estimates ofthe fabrication error. Therefore, an Integrated Non-Linearity (INL)error and a Differential Non-Linearity (DNL) error may be reduced and adigital-analog converter of high resolution may be realized.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. An apparatus for digital-analog conversion, theapparatus comprising: a first cell matrix configured to output a currentof a signal corresponding to a number of Most Significant Bits (MSBs) ofan input digital signal; a second cell matrix configured to output acurrent of a signal corresponding to a number of Least Significant Bits(LSBs) of the input digital signal; an amplifier configured to amplifythe output current of the second cell matrix at a preset amplification;an adder configured to add the output current of the first cell matrixand the output current of the amplifier; and an error detectorconfigured to detect a fabrication error, when the apparatus is turnedon, by comparing an amount of the output current of the adder with anamount of the output current of the first cell matrix, wherein the adderamplifies the output current of the second cell matrix.
 2. The apparatusof claim 1, wherein the error detector sets the current output to areference current when the first cell matrix drives one cell, whereinthe error detector determines a time when an amount of the outputcurrent of the amplifier is equal to an amount of the reference currentwhile changing the number of the cells driven in the second cell matrix,and wherein the error detector sets the fabrication error according to adifference between the number of the cells driven in the second cellmatrix and the total number of cells of the second cell matrix.
 3. Theapparatus of claim 1, wherein the error detector controls a bias currentsource supplied to the second cell matrix according to the detectedfabrication error.
 4. The apparatus of claim 1, further comprising: afirst decoder configured to receive the signal corresponding to thenumber of the MSBs and to convert the input MSB signal to aconsecutive-bit signal indicating the number of the cells to drive; anda second decoder configured to receive the signal corresponding to thenumber of the LSBs and to convert the input LSB signal to aconsecutive-bit signal indicating the number of the cells to drive,wherein the second decoder corrects the input LSB signal using thefabrication error detected by the error detector.
 5. The apparatus ofclaim 4, further comprising: a first switching matrix configured toswitch a plurality of cells of the first cell matrix according to theconsecutive-bit signal converted by the first decoder; and a secondswitching matrix configured to switch a plurality of cells of the secondcell matrix according to the consecutive-bit signal converted by thesecond decoder.
 6. The apparatus of claim 1, wherein the first cellmatrix and the second cell matrix each comprise a plurality of subcellmatrixes which are symmetrical to each other about at least one of avertical axis and a horizontal axis, and wherein each of the pluralityof subcell matrixes comprises 2^(N)−1-ary cells when the correspondingcell matrix outputs a current corresponding to an N-bit signal.
 7. Theapparatus of claim 6, wherein the second cell matrix further comprisesat least one cell configured to correct the fabrication error.
 8. Theapparatus of claim 1, wherein, when the second cell matrix outputs thecurrent corresponding to an N-bit signal, the amplifier sets theamplification such that an amount of the output current of one cell ofthe first cell matrix is 2^(N) times greater than an amount of theoutput current of one cell of the second cell matrix.
 9. The apparatusof claim 1, wherein the adder is a current mirror which adds the outputcurrent of the amplifier to an output of the first cell matrix.
 10. Amethod of a digital-analog converter, the method comprising: dividing aninput digital signal into a Most Significant Bit (MSB) signalcorresponding to a number of MSBs and a Least Significant Bit (LSB)signal corresponding to a number of LSBs; outputting a current for theMSB signal using a first cell matrix; outputting a current for the LSBsignal using a second cell matrix; amplifying the output current usingthe second cell matrix at a preset amplification; adding the outputcurrent of the first cell matrix and the amplified output current andoutputting a result of the adding; and detecting a fabrication error,when the digital-analog converter is turned on, by comparing an amountof the output current of an adder with an amount of the output currentof the first cell matrix, wherein the adder amplifies the output currentof the second cell matrix.
 11. The method of claim 10, wherein thedetecting of the fabrication error comprises: setting the current outputto a reference current when the first cell matrix drives one cell;determining a time when an amount of the output current of the amplifieris equal to an amount of the reference current while changing the numberof the cells driven in the second cell matrix; and setting thefabrication error according to a difference between a number of thecells driven in the second cell matrix and a total number of cells ofthe second cell matrix at the determined time.
 12. The method of claim10, further comprising: controlling a bias current source supplied tothe second cell matrix according to the detected fabrication error. 13.The method of claim 10, further comprising: converting the MSB signalinto a consecutive-bit signal indicating a number of the cells to bedriven of the first cell matrix using a first decoder; and convertingthe LSB signal to a consecutive-bit signal indicating a number of thecells to be driven of the second cell matrix using a second decoder,wherein, when the signal of the certain number of the LSBs is convertedto the consecutive-bit signal, the LSB signal is corrected using thedetected fabrication error.
 14. The method of claim 13, furthercomprising: switching a plurality of cells of the first cell matrixusing a first switching matrix according to the consecutive-bit signalconverted by the first decoder; and switching a plurality of cells ofthe second cell matrix using a second switching matrix according to theconsecutive-bit signal converted by the second decoder.
 15. The methodof claim 10, wherein the first cell matrix and the second cell matrixeach comprise a plurality of subcell matrixes which are symmetrical toeach other about at least one of a vertical axis and a horizontal axis,and wherein each of the plurality of subcell matrixes comprises2^(N)−1-ary cells when the corresponding cell matrix outputs a currentcorresponding to an N-bit signal.
 16. The method of claim 15, whereinthe second cell matrix further comprises at least one cell forcorrecting the fabrication error.
 17. The method of claim 10, wherein,when the second cell matrix outputs the current for the LSB signal, theamplification is determined such that an amount of the output current ofone cell of the first cell matrix is 2^(N) times greater than an amountof the output current of one cell of the second cell matrix.
 18. Themethod of claim 10, wherein the adding and outputting of the outputcurrent of the first cell matrix and the amplified output currentcomprises: adding the amplified output current to an output of the firstcell matrix using a current mirror.